Les Mikesell wrote:
> Johan Ehnberg wrote:
>>> OK. I can see now why this is true. But it seems like one could
>>> rewrite the backuppc rsync protocol to check the pool for a file with
>>> same checksum  before syncing. This could give some real speedup on
>>> long files. This would be possible at least for the cpool where the
>>> rsync checksums (and full file checksums) are stored at the end of
>>> each file.
>> Now this would be quite the feature - and it fits perfecty with the idea 
>> of smart pooling that BackupPC has. The effects are rather interesting:
>>
>> - Different incremental levels won't be needed to preserve bandwidth
>> - Full backups will indirectly use earlier incrementals as reference
>>
>> Definite whishlist item.
> 
> But you'll have to read through millions of files and the common case of 
> a growing logfile isn't going to find a match anyway.  The only way this 
> could work is if the remote rsync could send a starting hash matching 
> the one used to construct the pool filenames - and then you still have 
> to deal with the odds of collisions.
> 

Sure you are pointing to something and are right. What I don't see is 
why we'd have to do an (extra?) read through millions of files? That is 
done with every full anyway, and in the case of an incremental it would 
only be necessary for new/changed files. It would in fact also speed up 
those logs because of rotation: an old log changes name but is still 
found on the server. Same applies for the painful (for remote backups) 
moved big directories.

I suspect there is no problem in getting the hash with some tuning to 
Rsync::Perl? It's just a command as long as the protocol allows it.

Are collisions aren't exactly a performance problem? BackupPC handles 
them nicely from what I've seen.

/johan

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